Optimal electro-rheological clutch performance requires the gap between plates be as small as possible. This increases the available electro-rheological torque. Small gaps, however, increase the risk of contact between plates. Contact between any of the two sets of plates, or shorting, would eliminate the voltage potential between the sets of plates, eliminating the electro-rheological effect of the clutch. Only a slight amount of distortion of one of the plates could have this effect. Thermal stresses within the plates at elevated temperatures could produce such distortion. Small plate gaps are also a disadvantage when there is no voltage potential between the plates. Small gaps increase the conventional viscous effects, resulting in increased viscous drag and heat generation.